How to make a game drive on Linux?

(CachyOS/Arch) I have a 2TB SATA drive I want to convert from NTFS to ext4, and I have already formatted the drive with gparted.

However, I can't add then add a folder to that drive to then add in Steam as an installation location.

I am able to elevate to administrator via 'Open as Administrator' in Dolphin to then make a folder in the root directory for my Steam games, but then I get the 'Steam library folder is not writable' in the dialogue to add a directory in Steam.

Any idea where to go from here?